Earlier quoted context omitted.
People learn languages for a variety of purposes. Some people just want to know enough to be able to ask where the bathroom is and read a menu at a resturant.
Except you won't be able to do that with Duolingo. I'll go as far as saying that Duolingo is (very) negative for learners: it sells them the idea they are learning a language and progressing when they are in fact not. A good example of that is a comment I read here on HN from a user defending Duolingo since it allowed him to master hiragana (one script of Japanese) after two years and half. This is normally taking a…
First, you don't need 10k kanji to read. About 3000-5000 depending on what you read is enough. Then count 400-500 kanji per year if learning at university and being motivated (lot of people stops).
For conversation count two intensive years for the bare minimum, add one for more fluency. Actually all depends on how much effort you spend on it, I know a guy who was JLPT N2 or so after it's first university year (needless to say, he spent an aweful amount of time practicing, especially with natives). Then add at least one year in Japan to really get a good grasp (I went from N3 to N2 in a year while basically partying).